Retarder and circular polarizer

ABSTRACT

A retarder comprising a substrate, a first optically anisotropic layer formed of a composition comprising a rod-like liquid-crystal compound substantially generating a phase difference of π at 550 nm, and a second optically anisotropic layer formed of a composition comprising a rod-like liquid-crystal compound substantially generating a phase difference of π/2 at 550 nm is disclosed. At least either one of the rod-like liquid-crystal compounds is denoted by Formula (I) Q 1 -L 1 -A 1 -L 3 -M-L 4 -A 2 -L 2 -Q 2 : where Q 1  and Q 2  denote polymerizable groups; L 1  to L 4  denote single bonds or divalent linking groups provided that at least either of L 3  and L 4  represents —O—CO—O—; A 1  and A 2  denote C2-20 spacer groups and M denotes a mesogen group; and an in-plane slow axis of the second layer and an in-plane slow axis of the first layer cross substantially at 60 degrees.

FIELD OF THE INVENTION

The present invention relates to a retarder useful as a quarter waveplate used for reflective-type liquid-crystal display devices, writepickups for optical disks, or anti-reflective films. In particular, thepresent invention relates to a retarder comprising two opticallyanisotropic layers which can be respectively prepared by applying acomposition comprising a rod-like liquid-crystal compound on or above asurface of a substrate, and a circular polarizer which can be preparedby lamination of the retarder and a linear polarizing film in aroll-to-roll manner.

RELATED ART

Quarter wave plates can be used for various purposes and have alreadybeen practically used. However, most of quarter wave plates achieve λ/4only at a specific wavelength though they are called quarter waveplates. JPA No. 1998-68816 and JPA No. 1998-90521 (the term “JPA” asused herein means an “unexamined published Japanese patent application”)disclose retarders obtained by laminating two optically anisotropicpolymer films. In the retarder described in JPA No. 1998-68816, aquarter-wave plate generating a quarter wavelength phase difference anda half-wave plate generating a half wavelength phase difference arelaminated so that their optic axes are crossed. In the retarderdescribed in JPA No. 1998-90521, at least two retarders having aretardation value of 160-320 nm are laminated at an angle such thattheir slow axes are neither parallel nor orthogonal to each other. Theretarders described in both documents specifically having laminatestructures of two polymer films. Both documents explain that λ/4 can beachieved in a wide wavelength region by such retarders. However, thepreparation processes of the retarders described in JPA No. 1998-68816and JPA No. 1998-90521 require cutting two polymer films at apredetermined angle and laminating the resulting chips in order tocontrol the optical directions (optic axes or slow axes) of the twopolymer films. Such processes including laminating the resulting chipsare complex and have other disadvantages such as liability to qualityfailure due to misalignment, decrease in yield, increase in cost andliability to deterioration due to contamination. Moreover, it isdifficult to strictly adjust the retardation value of polymer films to adesired value.

On the other hand, a broadband quarter wave plate comprising at leasttwo optically anisotropic layers respectively formed of a liquid-crystalcompound are disclosed in JPA No. 2001-4837, JPA No. 2001-21720 and JPANo. 2000-206331. Especially, the technique disclosed in JPA No.2001-4837, in which the same liquid-crystal compounds can be used in theoptically anisotropic layers, is also attractive in terms of productioncosts. Quarter wave plate is generally integrated with a linearpolarizer film and incorporated into reflective-type, liquid-crystaldisplay devices as a component of a circular polarizer, so thatproductivity of the circular polarizer plate may remarkably be improvedif the circular polarizer can be prepared in such a way that the quarterwave plate as described in the aforementioned Publications or the like,which is prepared by applying a liquid-crystal compound to a surface ofa long substrate, is laminated with a long polarizer film in aroll-to-roll manner to thereby continuously produce a rolled-longcircular polarizer plate.

Investigations by the present inventors, however, revealed that layersformed of aligned rod-like molecules of the conventional liquid-crystalcompounds tend to have defects or to lower in-plane accuracy of theliquid-crystal orientation as the bandwidth of a retarder becomes to bewider. It was also found that the optical axis of one of theliquid-crystal molecular layer disclosed in the JPA No. 2001-4837required an alignment layer rubbed at an angle of as large as 75 degreesrelative to the longitudinal direction of the substrate, and this waslikely to lower accuracy in the liquid-crystal orientation. Extensivestudies on the causes of these problems by the present inventorsrevealed that the former problem was ascribable to a low solubility ofthe rod-like liquid-crystal compound, and the latter was ascribable tothat the rubbing of the alignment layer at an angle of 75 degrees couldnot produce a sufficient restrictive force on the orientation ofliquid-crystal molecules. Additionally we found that for obtaining halfwave plates or quarter wave plates, rod-like molecules of theliquid-crystal compounds employed in them are required to be alignedhomogeneously with a high degree of accuracy, however, the rod-likeliquid-crystal molecules tend to be tilted in various directions at anarea near to an air-interface. And such tendency is a factor of thelater problem.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a retarder and acircular polarizer capable of functioning in a broad band, that is, inthe visible light wave length region, of contributing to thinning and ofcontributing to reduction of planar defects occurring as a side effectwith widening bandwidth. Other object of the present invention is toprovide a circular polarizer readily producible by roll-to-rolllaminating of the retarder with a polarizer film. Other object of thepresent invention is to provide a circular polarizer contributing toimprovement in image quality of the displayed images when applied to anyimage display devices.

In one aspect, the present invention provides a retarder comprising:

a substrate, and on or above the substrate

a first optically anisotropic layer formed of a composition comprising arod-like liquid-crystal compound, in which the rod-like molecules arealigned homogeneously, and substantially generating a phase differenceof π at 550 nm, and

a second optically anisotropic layer formed of a composition comprisinga rod-like liquid-crystal compound, in which the rod-like molecules arealigned homogeneously, and substantially generating a phase differenceof π/2 at 550 nm;

wherein at least one of the rod-like liquid-crystal compounds is denotedby Formula (I) below;Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²  Formula (I)

where, Q¹ and Q² respectively denote a polymerizable group; L¹, L², L³and L⁴ respectively denote a single bond or a divalent linking groupprovided that at least either of L³ and L⁴ represents —O—CO—O—; A¹ andA² respectively denote C2-20 spacer group, and M denotes a mesogengroup; and

an in-plane slow axis of the second optically anisotropic layer and anin-plane slow axis of the first optically anisotropic layer crosssubstantially at 60 degrees.

As embodiments of the present invention, there are provided the retarderwherein M in the Formula (I) is a group denoted by —(—W¹-L⁵)_(n)-W²—,where W¹ and W² respectively denote a divalent alicyclic group, divalentaromatic group or divalent heterocyclic group; L⁵ denotes a single bondor a linking group; and n is 1, 2 or 3; the retarder wherein thesubstrate has a longitudinal direction, the in-plane slow axis of thefirst optically anisotropic layer and the longitudinal direction of thetransparent substrate cross substantially at +30 degrees; and thein-plane slow axis of the second optically anisotropic layer and thelongitudinal direction of the transparent substrate cross substantiallyat −30 degrees; the retarder wherein a rubbing axis for predeterminingan orientation angle of the rod-like molecules in the first opticallyanisotropic layer and the longitudinal direction of the transparentsubstrate cross substantially at 30 degrees, and a rubbing axis forpredetermining an orientation angle of the rod-like molecules in thesecond optically anisotropic layer and the longitudinal direction of thetransparent substrate cross substantially at −30 degrees; the retarderwherein a surface of the first optically anisotropic layer has therubbing axis for predetermining an orientation angle of the rod-likemolecules in the second optically anisotropic layer; and the retarderwherein at least one of the optically anisotropic layers comprises acompound denoted by Formula (V):(Hb-L²-)_(n)B¹  Formula (V)

where Hb denotes a C6-40 aliphatic group or oligosiloxanoxy group havinga C4-40 aliphatic group; L² represents a divalent linking group selectedfrom the group consisting of —O—, —S—, —CO—, —NR⁵—, —SO₂—, an alkylenegroup, alkenylene group, arylene group and any combinations thereof; R⁵represents a hydrogen atom or a C1-6 alkyl group; n represents aninteger from 2 to 12; and B¹ represents an n-valent group containing atleast three cyclic structures, so that the rod-like molecules in thelayer are aligned homogenously with a not greater than 10 degrees tiltangle relative to a layer plane.

In another aspect, the present invention provides a circular polarizercomprising:

a linear polarizer film having a transparent axis substantially inclinedat +45 degrees or −45 degrees relative to a longitudinal directionthereof,

a substrate having a longitudinal direction,

a first optically anisotropic layer formed of a composition comprising arod-like liquid-crystal compound, in which the rod-like molecules arealigned homogeneously, and substantially generating a phase differenceof π at 550 nm, and

a second optically anisotropic layer formed of a composition comprisinga rod-like liquid-crystal compound, in which the rod-like molecules arealigned homogeneously, and substantially generating a phase differenceof π/2 at 550 nm;

wherein at least one of the rod-like liquid-crystal compounds is denotedby Formula (I) below;Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²  Formula (I)

where, Q¹ and Q² respectively denote a polymerizable group; L¹, L², L³and L⁴ respectively denote a single bond or a divalent linking groupprovided that at least either of L³ and L⁴ represents —O—CO—O—; A¹ andA² respectively denote a C2-20 spacer group, and M denotes a mesogengroup;

the transparent axis of the linear polarizer film and the longitudinaldirection of the substrate cross substantially at +45 degrees or −45degrees; and

an in-plane slow axis of the second optically anisotropic layer and anin-plane slow axis of the first optically anisotropic layer crosssubstantially at 60 degrees.

As embodiments of the present invention, there are provided the circularpolarizer wherein M in the Formula (I) is a group denoted by denotes isdenoted by —(—W¹-L⁵)_(n)-W²—, where W¹ and W² respectively denote adivalent alicyclic group, divalent aromatic group or divalentheterocyclic group; L⁵ denotes a single bond or a linking group; and nis 1, 2 or 3; the circular polarizer wherein the in-plane slow axis ofthe first optically anisotropic layer and a longitudinal direction ofthe substrate cross substantially at +30 degrees and the in-plane slowaxis of the second optically anisotropic layer and the longitudinaldirection of the substrate cross substantially at −30 degrees; thecircular polarizer wherein a rubbing axis for predetermining anorientation angle of the rod-like molecules in the first opticallyanisotropic layer and the longitudinal direction of the substrate crosssubstantially at +30 degrees; and a rubbing axis for predetermining anorientation angle of the rod-like molecules in the second opticallyanisotropic layer and the longitudinal direction of the substrate crosssubstantially at −30 degrees; the circular polarizer wherein a surfaceof the first optically anisotropic layer has the rubbing axis forpredetermining an orientation angle of the rod-like molecules in thesecond optically anisotropic layer; and the retarder wherein at leastone of the optically anisotropic layers comprises a compound denoted byFormula (V):(Hb-L²-)_(n)B¹  Formula (V)

where Hb denotes a C6-40 aliphatic group or oligosiloxanoxy group havinga C4-40 aliphatic group; L² represents a divalent linking group selectedfrom the group consisting of —O—, —S—, —CO—, —NR⁵—, —SO₂—, an alkylenegroup, alkenylene group, arylene group and any combinations thereof; R⁵represents a hydrogen atom or a C1-6 alkyl group; n represents aninteger from 2 to 12; and B¹ represents an n-valent group containing atleast three cyclic structures, so that the rod-like molecules in thelayer are tilted at not greater than 10 degrees relative to a layerplane.

In the present specification, the term of “substantially” for an anglemeans that the angle is in the range of an exact angle ±5°. Preferably,the difference from the exact angle is less than 4°, and more preferablyless than 3°. In the present specification, signs of “+” and “−” for theangle do not limit the rightward direction and leftward directionrespectively, and are used for only relatively expressing angles indirections differing with each other. In the present specification, “aslow axis” means a direction showing a maximum refractive index.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an exemplary retarder of the presentinvention.

FIG. 2 is a schematic drawing of a circular polarizer plate of thepresent invention.

FIG. 3 is a schematic plan view showing an exemplary process of obliquestretching of a polymer film in the method of the present invention.

FIG. 4 is a schematic plan view showing another exemplary process ofoblique stretching of a polymer film in the method of the presentinvention.

FIG. 5 is a schematic plan view showing another exemplary process ofoblique stretching of a polymer film in the method of the presentinvention.

FIG. 6 is a schematic plan view showing another exemplary process ofoblique stretching of a polymer film in the method of the presentinvention.

FIG. 7 is a schematic plan view showing another exemplary process ofoblique stretching of a polymer film in the method of the presentinvention.

FIG. 8 is a schematic plan view showing another exemplary process ofoblique stretching of a polymer film in the method of the presentinvention.

FIG. 9 is a schematic plan view showing an exemplary punching processfor producing conventional polarizer plates.

FIG. 10 is a schematic plan view showing an exemplary punching processfor producing 45 degrees polarizer plates for use in the presentinvention.

FIG. 11 is a schematic sectional view showing an exemplary layerconstitution of the circular polarizer plate of the present invention.

FIG. 12 is a schematic sectional view showing another exemplary layerconstitution of the circular polarizer plate of the present invention.

FIG. 13 is a schematic sectional view showing an exemplary layerconstitution of the circular polarizer plate fabricated in Example 4.

DETAILED DESCRIPTION OF THE INVENTION

[Optical Characteristics of Retarder]

The retarder of the present invention comprises a first opticallyanisotropic layer formed of a composition comprising a liquid-crystalcompound, in which the rod-like molecules are aligned homogeneously; anda second optically anisotropic layer formed of a composition comprisinga liquid-crystal compound, in which the rod-like molecules are alignedhomogeneously. One of these two optically anisotropic layers maygenerate a phase difference of π substantially at a specific wavelength,and the other may generate a phase difference of π/2 substantially atthe wavelength. In order to obtain a π phase difference at a wavelength(λ) through an optically anisotropic layer, it is necessary to preparethe layer so as to adjust the measured retardation of the layer to λ/2at the λ. In order to obtain a π/2 phase difference at a wavelength (λ)through an optically anisotropic layer, it is necessary to prepare thelayer so as to adjust the measured retardation of the layer to λ/4 atthe λ. It is preferable that the optically anisotropic layers cangenerate π and π/2 phase differences respectively at 550 nm, which ismostly the middle of visible light range. That is, the first opticallyanisotropic layer desirably has a retardation in the range from 240 to290 nm, preferably from 250 to 280 nm, at 550 nm. The second opticallyanisotropic layer desirably has a retardation in the range from 110 to145 nm, preferably from 120 to 140 nm, at 550 nm.

In the specification, a retardation (Re) of an anisotropic layer meansan in-pale retardation when light incident along the normal linedirection of the layer. Specifically, a retardation is the value definedby the following formula:Re=(nx−ny)×d

In the formula, nx and ny denote the in-plane major refractive indexesof the optically anisotropic layer, and d (nm) denotes the thickness ofthe layer.

The thickness of the first and second optically anisotropic layers canarbitrarily be determined within a range in which the individual layerscan exhibit desired retardation values. In an exemplary case where thelayers are prepared with an identical species of rod-like liquid-crystalcompound, the thickness of the first optically anisotropic layergenerating a phase difference of π is preferably twice as thick as thethickness of the second optically anisotropic layer generating a phasedifference of π/2. Although preferable ranges for the thickness of theindividual optically anisotropic layers may differ depending on therod-like liquid-crystal compounds to be used, it is preferably 0.1 to 10micro meters in general, more preferably 0.2 to 8 micro meters, andstill more preferably 0.5 to 5 micro meters. According to the presentinvention, the retarder is successfully thinned by forming theindividual optically anisotropic layers so as to align homogeneously theliquid-crystal molecules contained therein.

It is to be noted now that the term of “homogeneous alignment” in thecontext of the present specification is used for not only homogeneousalignment in an absolute sense but also for any alignments inclined at atilt angle of 10 degrees or around.

[Constitutions of Retarder and Circular Polarizer Plate]

FIG. 1 is a schematic drawing showing a representative constitution ofthe retarder of the present invention. As shown in FIG. 1, the basicretarder of the present invention comprises a long transparent substrate(S) and the first optically anisotropic layer (A), and further comprisesthe second optically anisotropic layer (B). The first opticallyanisotropic layer (A) generates a phase difference of π. The secondoptically anisotropic layer (B) generates a phase difference of π/2. Thelongitudinal direction of the substrate (S) and the slow axis (a) of thefirst optically anisotropic layer (A) cross at 30 degrees. The slow axis(b) of the second optically anisotropic layer (B) and the slow axis (a)of the first optically anisotropic layer (A) cross at an angle (γ) of 60degrees. Both of the first and second optically anisotropic layers (A)and (B) shown in FIG. 1 respectively contain rod-like liquid-crystalmolecules (c1 and c2). The rod-like liquid-crystal molecules c1 and c2are aligned homogeneously. The longitudinal axes of the rod-like,liquid-crystal molecules (c1 and c2) correspond to the slow axes (a andb) of the optically anisotropic layers.

FIG. 2 is a schematic drawing showing a representative constitution ofthe circular polarizer of the present invention. The circular polarizershown in FIG. 2 comprises the transparent substrate (S), the first andsecond optically anisotropic layers (A) and (B) as same as shown in FIG.1, and further comprises a polarizer film (P). The polarizingtransparent axis (p) of the polarizer film (P) and the longitudinaldirection (s) of the transparent substrate (S) cross at 45 degrees, thepolarizing transparent axis (p) and the slow axis (a) of the firstoptically anisotropic layer (A) cross at 15 degrees, and similar to asillustrated in FIG. 1, the slow axis (a) of the first opticallyanisotropic layer (A) and the slow axis (b) of the second opticallyanisotropic layer (B) cross at 60 degrees. Also the first opticallyanisotropic layer (A) and the second optically anisotropic layer (B)shown in FIG. 2 respectively contain the rod-like liquid-crystalmolecules (c1 and c2). The rod-like liquid-crystal molecules (c1 and c2)are aligned homogeneously. The longitudinal axes of the rod-likeliquid-crystal molecules (c1 and c2) correspond to the in-plane slowaxes (a and b) of the optically anisotropic layers (A and B).

For the convenience sake, exemplary constitutions of the retarder andcircular polarizer plate in which the first optically anisotropic layer(A) (phase difference=π) is disposed closer to the transparent substrate(S) and the second optically anisotropic layer (B) (phasedifference=π/2) is disposed on the outer side are respectively shown inFIG. 1 and FIG. 2, it is also allowable to change the positions of thefirst and second optically anisotropic layers (A) and (B). A preferableconstitution is, however, such as disposing the first opticallyanisotropic layer (A) (phase difference=π) closer to the transparentsubstrate (S) and the second optically anisotropic layer (B) (phasedifference=π/2) on the outer side.

[Optically Anisotropic Layer]

In the retarder and circular polarizer plate of the present invention, arod-like liquid-crystal compound denoted by the formula (I) below isused for preparing at least one of the first and second opticallyanisotropic layers. It is also allowable to use the rod-likeliquid-crystal compound denoted by the formula (I) below for both of theoptically anisotropic layers. The rod-like liquid-crystal compounds usedin the first and second optically anisotropic layers may be identical ordifferent each other.Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²  Formula (I)

In the Formula (I), Q¹ and Q² respectively denote a polymerizable group;L¹, L², L³ and L⁴ respectively denote a single bond or a divalentlinking group provided that at least either of L³ and L⁴ denotes—O—CO—O—. A¹ and A² respectively denote a C2-20 spacer group; and Mdenotes a mesogen group.

The polymerizable rod-like liquid-crystal compound denoted by theformula (I) will be described in detail.

In the formula (I), Q¹ and Q² respectively denote a polymerizable group.The polymerizable groups may be addition polymerizable (ring openingpolymerizable) or condensation polymerizable. Preferably, Q¹ and Q²respectively denote a group capable of addition polymerization orcondensation polymerization. The examples of the polymerizable groupsare shown below.

The divalent linking group respectively denoted by L¹, L², L³ and L⁴ ispreferably the one selected from the group consisting of —O—, —S—, —CO—,—NR²—, —CO—O—, —O—CO—O—, —CO—NR²—, —NR²—CO—, —O—CO—, —O—CO—NR²—,—NR²—CO—O—, —NR²—CO—NR²— and single bond. R² represents a C1-7 alkylgroup or a hydrogen atom. At least either of L³ and L⁴ expresses—O—CO—O— (carbonate group).

Among groups denoted by a combination of Q¹ and L¹ or by a combinationof Q² and L², the preferable examples include CH₂═CH—CO—O—,CH₂═C(CH₃)—CO—O— and CH₂═C(Cl)—CO—O—, and more preferable example isCH₂═CH—CO—O—.

A¹ and A² respectively denote a C2-20 spacer group, and preferably C2-12aliphatic group, and more preferably alkylene group. The spacer group ispreferably a chain group, and may contain oxygen atoms or sulfur atomsnot adjacent with each other. The spacer group may have a substitutivegroup, and may more specifically be substituted by a halogen atom(fluorine, chlorine, bromine), cyano, methyl or ethyl.

The mesogen group denoted by M may selected from any known mesogengroups. The preferable examples thereof are denoted by the formula (II)below.—(—W¹-L⁵)_(n)-W²—  Formula (II)

In the Formula (II), W¹ and W² respectively denote a divalent alicyclicgroup, divalent aromatic group or divalent heterocyclic group. L⁵ is asingle bond or a linking group, and the linking group. The examples ofthe linking group denoted by L⁵ include those shown as the specificexamples denoted by L¹ to L⁴ in the above-described the formula (I),CH₂—O— and —O—CH₂—. “n” is an integer of 1, 2 or 3.

The examples of W¹ and W² include cyclohexane-1,4-diyl, 1,4-phenylene,pyrimidine-2,5-diyl, pyridine-2,5-diyl, 1,3,4-thiadiazole-2,5-diyl,1,3,4-oxathiadiazole-2,5-diyl, naphthalene-2,6-diyl,naphthalene-1,5-diyl, thiophene-2,5-diyl and pyridazine-3,6-diyl.1,4-Cyclohexanediyl may exist in trans- and cis-stereoisomers, whereeither of them, and any mixture in an arbitrary mixing ratio can be usedin the present invention. The trans form is more preferable. W¹ and W²may independently have substitutive group, and the specific examples ofthe substitutive group include halogen atom (fluorine, chlorine,bromine, iodine), cyano, C1-10 alkyl groups (e.g., methyl, ethyl,propyl), C1-10 alkoxy groups (e.g., methoxy, ethoxy), C1-10 acyl groups(e.g., formyl, acetyl), C1-10 alkoxycarbonyl groups (e.g.,methoxycarbonyl, ethoxycarbonyl), C1-10 acyloxy groups (e.g., acetyloxy,propionyloxy), nitro, trifluoromethyl, and difluoromethyl.

The preferable examples of the mesogen group denoted by theabove-described the formula (II) are shown below, however, the mesogengroup is not limited to these examples. The mesogen group may besubstituted by any substitutive groups described in the above.

The specific examples of the compounds denoted by the Formula (I) willbe shown below, where it is to be understood that the present inventionis by no means limited thereto.

The compounds denoted by the formula (I) may be synthesized by theprocesses described in Published Japanese Translation of PCTInternational Publication for Patent Applications No. 11-513019.

In the optically anisotropic layers, the rod-like molecules aredesirably aligned in a substantially uniformly manner, more desirablyfixed in a substantially uniformly aligned manner, and most preferablyfixed by polymerization reaction. According to the present invention,the rod-like molecules in the optically anisotropic layers are desirablyaligned in a manner such as an angle between the in-plane slow axis ofthe each optically anisotropic layer and the longitudinal direction ofthe transparent substrate is substantially +30 degrees or −30 degrees.The rod-like molecules in the optically anisotropic layers are desirablyaligned homogeneously.

Rod-like liquid-crystal compounds other than those denoted by theFormula (I) may be used in the combination with the compound denoted bythe Formula (I) for preparing the layers. The examples of such rod-likeliquid-crystal compounds include azomethines, azoxys, cyanobiphenyls,cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acidphenyl esters, cyanophenylcyclohexanes, cyano-substitutedphenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans and alkenylcyclohexyl benzonitriles. Not onlylow-molecular-weight liquid-crystal compounds as mentioned above butalso high-molecular-weight liquid-crystal compounds can be used.

The rod-like liquid-crystal molecules may be fixed in an alignment stateby polymerization. The examples of the polymerizable rod-likeliquid-crystal compound include those described in “Makromol. Chem.,Vol. 190, p. 2255(1989)”; “Advanced Materials Vol. 5, p. 107 (1993)”;U.S. Pat. Nos. 4,683,327, 5,622,648 and 5,770,107; InternationalPublications WO95/22,586, WO95/24,455, WO97/00,600, WO98/23,580 andWO98/52905; JPA No. 1989-272551, JPA No. 1994-16616, JPA No. 1995-110469and JPA No. 1999-80081; and Japanese Patent Application No. 2001-64627.

The optically anisotropic layers are desirably prepared by applying acomposition (coating solution) comprising a rod-like liquid-crystalcompound, and if necessary additives, to a surface of an alignmentlayer. Any organic solvents may be used for preparing the coatingsolution. The examples of the organic solvents include amides (e.g.,N,N-dimethyl formamide), sulfoxides (e.g., dimethyl sulfoxide),heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene,hexane), alkyl halides (e.g., chloroform, dichloromethane), esters(e.g., methyl acetate, butyl acetate), ketones (e.g., acetone, methylethyl ketone) and ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane).Alkyl halides and ketones are preferred. Two or more organic solventsmay be used in combination. The coating solution can be applied by knowntechniques (e.g., extrusion coating, direct gravure coating, reversegravure coating, die coating).

The rod-like molecules in the layers are desirably fixed in an alignmentstate, preferably fixed by the polymerization reaction of thepolymerizable groups included in the liquid-crystal molecules. Thepolymerization reaction may be carried out in a manner of a thermalpolymerization reaction with a thermal polymerization initiator or in amanner of a photo-polymerization reaction with a photo-polymerizationinitiator. Photo-polymerization reaction is preferred. The examples ofphoto-polymerization initiators include alpha-carbonyl compounds(described in U.S. Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers(described in U.S. Pat. No. 2,448,828), alpha-hydrocarbon-substitutedaromatic acyloin compounds (described in U.S. Pat. No. 2,722,512),polynuclear quinone compounds (described in U.S. Pat. Nos. 3,046,127 and2,951,758), combinations of triarylimidazole dimers and p-aminophenylketone (described in U.S. Pat. No. 3,549,367), acridine and phenazinecompounds (described in JPA No. 1985-105667 and U.S. Pat. No. 4,239,850)and oxadiazole compounds (described in U.S. Pat. No. 4,212,970).

The amount of the photo-polymerization initiator to be used ispreferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight onthe basis of solids in the coating solution. Irradiation forpolymerizing the liquid-crystal molecules preferably uses UV rays. Theirradiation energy is preferably 20 mJ/cm² to 50 J/cm², and morepreferably 100 to 800 mJ/cm². Irradiation may be performed under heatingto accelerate the photo-polymerization reaction.

The thickness of the optically anisotropic layer is preferably 0.1 to 10micro meters, more preferably 0.5 to 5 micro meters.

[Alignment Controlling Additives at Air Interface Side]

In general, rod-like liquid-crystal molecules can be alignedhomogenously in the area near to the alignment layer interface, and onthe other hand, they tend to be aligned with a certain level of tiltangles in the area near to the air interface. It is effective to use anadditive to suppress such their tendencies, and it is particularlypreferable to use the additives denoted by the formula (V) below. Theamount of the additive is desirably from 0.01 to 5 wt % with respect tothe amount of the liquid-crystal compound.(Hb-L⁵²-)_(n)B⁵¹  Formula (V)

In the Formula (V), Hb represents a C6-40 aliphatic group, oroligosiloxanoxy group having a C6-40 aliphatic group. Hb is preferably aC6-40 aliphatic group, more preferably a fluorine-substituted C6-40aliphatic group or a branched C6-40 aliphatic group, and most preferablya fluorine-substituted C6-40 alkyl group or a branched C6-40 alkylgroup.

Among the aliphatic groups, chain aliphatic groups are preferred torather than cyclic aliphatic groups. The chain aliphatic groups may havea straight or branched chain structure. The number of carbon atoms ofthe aliphatic group is preferably 7 to 35, more preferably 8 to 30,still more preferably 9 to 25, and most preferably 10 to 20.

In the specification, the term of “aliphatic group” is a general termfor a substituted or non-substituted alkyl group, substituted ornon-substituted alkenyl group and substituted or non-substituted alkynylgroup. The aliphatic group is desirably a substituted or non-substitutedalkyl group, or substituted or non-substituted alkenyl group, andpreferably a substituted or non-substituted alkyl group.

The examples of the substituent of the aliphatic group include halogenatoms, hydroxy, cyano, nitro, alkoxy group, substituted alkoxy group(e.g., oligoalkoxy group), alkenyloxy group (e.g., vinyloxy), acyl group(e.g., acryloyl, methacryloyl), acyloxy group (e.g., acryloyloxy,benzoyloxy), sulfamoyl group, sulfamoyl groups substituted withaliphatic groups and epoxy alkyl group (e.g., epoxy ethyl). Among them,halogen atoms are desirable, and fluorine is more desirable, assubstituent. Fluorinated aliphatic group is an aliphatic group in whichpart or all of the hydrogen atoms have been substituted with fluorineatoms. 50 to 100 percent of the hydrogen atoms in the aliphatic groupare desirably substituted with fluorine atoms, with 60 to 100 percentsubstitution being preferred, 80 to 100 percent substitution being ofeven greater preference and 85 to 100 percent substitution being of evenmuch greater preference.

The number of the carbon atoms included in the oligosiloxanoxy grouphaving an aliphatic group is desirably from 7 to 35, preferably from 8to 30, more preferably from 9 to 25 and much more preferably from 10 to20. The oligosiloxanoxy group having an aliphatic group can be denotedby the following formula:R⁵¹—(Si(R⁵²)₂—O)_(q)—.

In the formula, R⁵¹ is hydrogen, hydroxy or aliphatic group; R⁵² ishydrogen, aliphatic group or alkoxy group; and q is an integer from 1 to12. A chain aliphatic group is preferred to a cyclic aliphatic group asthe aliphatic group denoted by R⁵¹ or R⁵². The chain aliphatic group mayhave a straight chain or branched chain structure. The number of thecarbon atoms included in the aliphatic group is desirably from 1 to 12,preferably from 1 to 8, more preferably from 1 to 6 and much morepreferably from 1 to 4.

The aliphatic group denoted respectively by R⁵¹ or R⁵² is a substitutedor non-substituted alkyl group, substituted or non-substituted alkenylgroup, or substituted or non-substituted alkynyl group. As the aliphaticgroup, a non-substituted alkyl group, substituted alkyl group,non-substituted alkenyl group and substituted alkenyl group arepreferred, and a non-substituted and substituted alkyl group are morepreferred.

The aliphatic group denoted respectively by R⁵¹ or R⁵² may besubstituted with at least one of substituent such as a halogen atom,hydroxy, cyano, nitro, alkoxy group, substituted alkoxy group (e.g.,oligoalkoxy), alkenyloxy group (e.g., vinyloxy), acyl group (e.g.,acryloyl, methacryloyl), acyloxy group (e.g., acryloyl oxy, benzoyloxy), sulfamoyl, sulfamoyl group substituted with aliphatic group orepoxy alkyl group (e.g., epoxy ethyl).

The alkoxy group denoted by R⁵² may have a cyclic or straight orbranched chain structure. The number of the carbon atoms included in thealkoxy group is desirably from 1 to 12, preferably from 1 to 8, morepreferably from 1 to 6 and more preferably from 1 to 4.

The specific examples of Hb are shown below.

Hb1: n-C₁₆H₃₃—

Hb2: n-C₂₀H₄₁—

Hb3: n-C₆H₁₃—CH(n-C₄H₉)—CH₂—CH₂—

Hb4: n-C₁₂H₂₅—

Hb5: n-C₁₁H₃₇—

Hb6: n-C₁₄H₂₉—

Hb7: n-C₁₅H₃₁—

Hb8: n-C₁₀H₂₁—

Hb9: n-C₁₀H₂₁—CH(n-C₄H₉)—CH₂—CH₂—

Hb10: n-C₈F₁₇—

Hb11: n-C₈H₁₇—

Hb12: CH(CH₃)₂—{C₃H₆—CH(CH₃)}₃—C₂H₄—

-   -   Hb13: CH(CH₃)₂—{C₃H₆—CH(CH₃)}₂—C₃H₆—C(CH₃)═CH—CH₂—

Hb14: n-C₈H₁₇—CH(n-C₆H₁₃)—CH₂—CH₂—

Hb15: n-C₆H₁₃—CH(C₂H₅)—CH₂—CH₂—

Hb16: n-C₈F₁₇—CH(n-C₄F₉)—CH₂—

Hb17: n-C₈F₁₇—CF(n-C₆F₁₃)—CF₂—CF₂—

Hb18: n-C₃F₇—CF(CF₃)—CF₂—

Hb19: Si(CH₃)₃—{Si(CH₃)₂—O}₆—O—

Hb20: Si(OC₃H₇)(C₁₆F₃₃)(C₂H₄—SO₂—NH—C₈F₁₇)—O—

In the Formula (V), L⁵² is a single bond or divalent linking group. Thedivalent linking group is desirably a divalent linking group selectedfrom the group consisting of -alkylene-, -fluorinated alkylene-, —O—,—S—, —CO—, —NR—, —SO₂— and any combinations thereof. R is a hydrogenatom or C1-20 alkyl group. R is desirably a hydrogen atom or C1-12 alkylgroup. The number of the carbon atoms included in the alkylene or thefluorinated alkylene is desirably from 1 to 40, preferably from 1 to 30,more preferably from 1 to 20, much more preferably from 1 to 15 andfurther much more preferably from 1 to 12.

The specific examples of L⁵² are shown below. They are connected on theleft to Hb and on the right to B⁵¹.

L⁵²10: single bond

L⁵²11: —O—

L⁵²12: —O—CO—

L⁵²13: —CO—C₄H₈—O—

L⁵²14: —O—C₂H₄—O—C₂H₄—O—

L⁵²15: —S—

L⁵²16: —N(n-C₁₂H₂₅)—

L⁵²17: —SO₂—N(n-C₃H₇)—CH₂CH₂—O—

L⁵²18: —O—{CF(CF₃)—CF₂—O}₃—CF(CF₃)—

In the Formula (V), n is an integer from 2 to 12. n is desirably aninteger from 2 to 9, preferably from 2 to 6, more preferably 2, 3 or 4and much more preferably 3 or 4.

In the Formula (V), B⁵¹ is an n-valent group showing an excluded volumeeffect and comprising at least three rings. B⁵¹ is desirably an n-valentgroup denoted by Formula (V-a).(-Cy⁵¹-L⁵³-)_(n)Cy⁵²  Formula (V-a)

In the Formula (V-a), Cy⁵¹ is a divalent cyclic group. Cy⁵¹ is desirablya divalent aromatic hydrocarbon group or a divalent heterocyclicdivalent group and more preferably a divalent aromatic hydrocarbongroup.

In the specification, the term of “divalent aromatic hydrocarbon group”is a general term for a substituted or non-substituted arylene group.The examples of the arylene group include benzene-diyl, indene-diyl,naphthalene-diyl, fluorine-diyl, phenanthrene-diyl, anthracene-diyl andpyrane-diyl. The divalent aromatic hydrocarbon group is desirablybenzene-diyl or naphthalene-diyl.

The examples of the substituent of the substituted arylene group includean aliphatic group, aromatic hydrocarbon group, heterocyclic group,halogen atom, alkoxy group (e.g., methoxy, ethoxy, methoxy-ethoxy),aryloxy group (e.g., phenoxy), arylazo group (e.g., phenylazo),alkylthio group (e.g., methylthio, ethylthio, propylthio), alkylaminogroup (e.g., methylamino, propylamino), acyl group (e.g., acetyl,propanoyl, octanoyl, benzoyl), acyloxy group (e.g., acetoxy,pivaloyloxy, benzoyloxy), hydroxy, mercapto, amino, carboxy, sulfo,carbamoyl, sulfamoyl and ureido.

The divalent aromatic hydrocarbon group bonded to another aromatichydrocarbon group through a single, vinylene or ethynylene bond may showthe above-mentioned ability of promoting alignment of liquid-crystalmolecules. The divalent aromatic hydrocarbon group may have a group ofHb-L⁵²- as a substituent.

The hetero ring included in the divalent heterocyclic group denoted byCy⁵¹ is desirably five-, six- or seven-membered, preferably five- orsix-membered, and more preferably six-membered. The hetero atomconstituting the hetero ring is desirably nitrogen, oxygen or sulfur.The hetero ring desirably has aromaticity. Aromatic hetero rings areusually unsaturated rings and desirably has maximum double bondings. Theexamples of the hetero ring include a furan ring, thiophene ring,pyrrole ring, pyrroline ring, pyrrolizine ring, oxazole ring, isoxazolering, thiazole ring, isothiazole ring, imidazole ring, imidazoline ring,imidazolidine ring, pyrazole ring, pyrazolidine ring, triazole ring,furazan ring, tetrazole ring, pyrane ring, thiine ring, pyridine ring,piperidine ring, oxazine ring, morpholine ring, thiazine ring,pyridazine ring, pyrimidine ring, pyrazine ring, piperazine ring andtriazine ring.

The hetero rings may be condensed with other hetero rings, aliphaticrings or aryl rings. The examples of the condensed hetero rings includea benzofuran ring, isobenzofuran ring, benzothiophenering, indolering,indolinering, isoindole ring, benzoxazole ring, benzothiazole ring,indazole ring, benzoimidazole ring, chromene ring, chromane ring,isochromane ring, quinoline ring, isoquinoline ring, cinnoline ring,phthalazine ring, quinazoline ring, quinoxaline ring, di-benzofuranring, carbazole ring, xanthene ring, acridine ring, phenanthridine ring,phenanthroline ring, phenazine ring, phenoxazine ring, thianthrene ring,indolizine ring, quinolidine ring, quinuclidine ring, naphthridine ring,purine ring and pteridine ring.

The divalent heterocyclic group may have at least one substituent. Theexamples of the substituent for the divalent heterocyclic group areidentical with those for the substituted arylene group.

The divalent heterocyclic group, Cy⁵¹, may connected to the L⁵³ or thecyclic group denoted by Cy⁵², when L⁵³ is a single bond, through ahetero atom such as nitrogen constituting a piperidine ring. The heteroatom linking them may form an onium salt such as an oxonium, sulfoniumor ammonium.

The cyclic Cy⁵¹ and Cy⁵² may form a planar structure, that is, adiscotic structure, as a whole. In such a case, the above-mentionedability of promoting alignment of liquid-crystal molecules can beobtained.

The specific examples of Cy⁵¹ are shown below. When the plural groupscorresponding to Hb-L⁵²- are bonded to a divalent aromatic hydrocarbongroup or a divalent heterocyclic group, one of the plural groups can beregarded as Hb-L⁵²- and other can be regarded as substituent of thearomatic hydrocarbon group or the heterocyclic group.

The number of the carbon atoms included in the oligosiloxanoxy grouphaving an aliphatic group is desirably from 7 to 35, preferably from 8to 30, more preferably from 9 to 25 and much more preferably from 10 to20. The oligosiloxanoxy group having an aliphatic group can be denotedby the following formula:R⁵¹—(Si(R⁵²)₂—O)_(q)—.

In the formula, R⁵¹ is hydrogen, hydroxy or aliphatic group; R⁵² ishydrogen, aliphatic group or alkoxy group; and q is an integer from 1 to12. A chain aliphatic group is preferred to a cyclic aliphatic group asthe aliphatic group denoted by R⁵¹ or R⁵². The chain aliphatic group mayhave a straight chain or branched chain structure. The number of thecarbon atoms included in the aliphatic group is desirably from 1 to 12,preferably from 1 to 8, more preferably from 1 to 6 and much morepreferably from 1 to 4.

The aliphatic group denoted respectively by R⁵¹ or R⁵² is a substitutedor non-substituted alkyl group, substituted or non-substituted alkenylgroup, or substituted or non-substituted alkynyl group. As the aliphaticgroup, a non-substituted alkyl group, substituted alkyl group,non-substituted alkenyl group and substituted alkenyl group arepreferred, and a non-substituted and substituted alkyl group are morepreferred.

The aliphatic group denoted respectively by R⁵¹ or R⁵² may besubstituted with at least one of substituent such as a halogen atom,hydroxy, cyano, nitro, alkoxy group, substituted alkoxy group (e.g.,oligoalkoxy), alkenyloxy group (e.g., vinyloxy), acyl group (e.g.,acryloyl, methacryloyl), acyloxy group (e.g., acryloyl oxy, benzoyloxy), sulfamoyl, sulfamoyl group substituted with aliphatic group orepoxy alkyl group (e.g., epoxy ethyl).

The alkoxy group denoted by R⁵² may have a cyclic or straight orbranched chain structure. The number of the carbon atoms included in thealkoxy group is desirably from 1 to 12, preferably from 1 to 8, morepreferably from 1 to 6 and more preferably from 1 to 4.

The specific examples of Hb are shown below.

Hb1: n-C₁₆H₃₃—

Hb2: n-C₂₀H₄₁—

Hb3: n-C₆H₁₃—CH(n-C₄H₉)—CH₂—CH₂—

Hb4: n-C₁₂H₂₅—

Hb5: n-C₁₁H₃₇—

Hb6: n-C₁₄H₂₉—

Hb7: n-C₁₅H₃₁—

Hb8: n-C₁₀H₂₁—

Hb9: n-C₁₀H₂₁—CH(n-C₄H₉)—CH₂—CH₂—

Hb10: n-C₈F₁₇—

Hb11: n-C₈H₁₇—

Hb12: CH(CH₃)₂—{C₃H₆—CH(CH₃)}₃—C₂H₄—

Hb13: CH(CH₃)₂—{C₃H₆—CH(CH₃)}₂—C₃H₆—C(CH₃)═CH—CH₂—

Hb14: n-C₈H₁₇—CH(n-C₆H₁₃)—CH₂—CH₂—

Hb15: n-C₆H₁₃—CH(C₂H₅)—CH₂—CH₂—

Hb16: n-C₈F₁₇—CH(n-C₄F₉)—CH₂—

Hb17: n-C₈F₁₇—CF(n-C₆F₁₃)—CF₂—CF₂—

Hb18: n-C₃F₇—CF(CF₃)—CF₂—

Hb19: Si(CH₃)₃—{Si(CH₃)₂—O}₆—O—

Hb20: Si(OC₃H₇)(C₁₆F₃₃)(C₂H₄—SO₂—NH—C₈F₁₇)—O—

In the Formula (V), L⁵² is a single bond or divalent linking group. Thedivalent linking group is desirably a divalent linking group selectedfrom the group consisting of -alkylene-, -fluorinated alkylene-, —O—,—S—, —CO—, —NR—, —SO₂— and any combinations thereof. R is a hydrogenatom or C1-20 alkyl group. R is desirably a hydrogen atom or C1-12 alkylgroup. The number of the carbon atoms included in the alkylene or thefluorinated alkylene is desirably from 1 to 40, preferably from 1 to 30,more preferably from 1 to 20, much more preferably from 1 to 15 andfurther much more preferably from 1 to 12.

The specific examples of L⁵² are shown below. They are connected on theleft to Hb and on the right to B⁵¹.

L⁵²10: single bond

L⁵²11: —O—

L⁵²12: —O—CO—

L⁵²13: —CO—C₄H₈—O—

L⁵²14: —O—C₂H₄—O—C₂H₄—O—

L⁵²15: —S—

L⁵²16: —N(n-C₁₂H₂₅)—

-   -   L⁵²17: —SO₂—N(n-C₃H₇)—CH₂CH₂—O—

L⁵²18: —O—{CF(CF₃)—CF₂—O}₃—CF(CF₃)—

In the Formula (V), n is an integer from 2 to 12. n is desirably aninteger from 2 to 9, preferably from 2 to 6, more preferably 2, 3 or 4and much more preferably 3 or 4.

In the Formula (V), B⁵¹ is an n-valent group showing an excluded volumeeffect and comprising at least three rings. B⁵¹ is desirably an n-valentgroup denoted by Formula (V-a).(-Cy⁵¹-L⁵³-)_(n)Cy⁵²  Formula (V-a)

In the Formula (V-a), Cy⁵¹ is a divalent cyclic group. Cy⁵¹ is desirablya divalent aromatic hydrocarbon group or a divalent heterocyclicdivalent group and more preferably a divalent aromatic hydrocarbongroup.

The divalent aromatic hydrocarbon group is a general term for asubstituted or non-substituted arylene group. The examples of thearylene group include benzene-diyl, indene-diyl, naphthalene-diyl,fluorine-diyl, phenanthrene-diyl, anthracene-diyl and pyrane-diyl. Thedivalent aromatic hydrocarbon group is desirably benzene-diyl ornaphthalene-diyl.

The examples of the substituent of the substituted arylene group includean aliphatic group, aromatic hydrocarbon group, heterocyclic group,halogen atom, alkoxy group (e.g., methoxy, ethoxy, methoxy-ethoxy),aryloxy group (e.g., phenoxy), arylazo group (e.g., phenylazo),alkylthio group (e.g., methylthio, ethylthio, propylthio), alkylaminogroup (e.g., methylamino, propylamino), acyl group (e.g., acetyl,propanoyl, octanoyl, benzoyl), acyloxy group (e.g., acetoxy,pivaloyloxy, benzoyloxy), hydroxy, mercapto, amino, carboxy, sulfo,carbamoyl, sulfamoyl and ureido.

The divalent aromatic hydrocarbon group bonded to another aromatichydrocarbon group through a single, vinylene or ethynylene bond may showthe above-mentioned ability of promoting alignment of liquid-crystalmolecules. The divalent aromatic hydrocarbon group may have a group ofHb-L⁵²- as a substituent.

The hetero ring included in the divalent heterocyclic group denoted byCy⁵¹ is desirably five-, six- or seven-membered, preferably five- orsix-membered, and more preferably six-membered. The hetero atomconstituting the hetero ring is desirably nitrogen, oxygen or sulfur.The hetero ring desirably has aromaticity. Aromatic hetero rings areusually unsaturated rings and desirably has maximum double bondings. Theexamples of the hetero ring include a furan ring, thiophene ring,pyrrole ring, pyrroline ring, pyrrolizine ring, oxazole ring, isoxazolering, thiazole ring, isothiazole ring, imidazole ring, imidazoline ring,imidazolidine ring, pyrazole ring, pyrazolidine ring, triazole ring,furazan ring, tetrazole ring, pyrane ring, thiine ring, pyridine ring,piperidine ring, oxazine ring, morpholine ring, thiazine ring,pyridazine ring, pyrimidine ring, pyrazine ring, piperazine ring andtriazine ring.

The hetero rings may be condensed with other hetero rings, aliphaticrings or aryl rings. The examples of the condensed hetero rings includea benzofuran ring, isobenzofuran ring, benzothiophene ring, indole ring,indoline ring, isoindole ring, benzoxazole ring, benzothiazole ring,indazole ring, benzoimidazole ring, chromene ring, chromane ring,isochromane ring, quinoline ring, isoquinoline ring, cinnoline ring,phthalazine ring, quinazoline ring, quinoxaline ring, di-benzofuranring, carbazole ring, xanthene ring, acridine ring, phenanthridine ring,phenanthroline ring, phenazine ring, phenoxazine ring, thianthrene ring,indolizine ring, quinolidine ring, quinuclidine ring, naphthridine ring,purine ring and pteridine ring.

The divalent heterocyclic group may have at least one substituent. Theexamples of the substituent for the divalent heterocyclic group areidentical with those for the substituted arylene group.

The divalent heterocyclic group, Cy⁵¹, may connected to the L⁵³ or thecyclic group denoted by Cy⁵², when L⁵³ is a single bond, through ahetero atom such as nitrogen constituting a piperidine ring. The heteroatom linking them may form an onium salt such as an oxonium, sulfoniumor ammonium.

The cyclic Cy⁵¹ and Cy⁵² may form a planar structure, that is, adiscotic structure, as a whole. In such a case, the above-mentionedability of promoting alignment of liquid-crystal molecules can beobtained.

The specific examples of Cy⁵¹ are shown below. When the plural groupscorresponding to Hb-L⁵²- are bonded to a divalent aromatic hydrocarbongroup or a divalent heterocyclic group, one of the plural groups can beregarded as Hb-L⁵²- and others can be regarded as substituent of thearomatic hydrocarbon group or the heterocyclic group.

In the Formula (V-a), L⁵³ is a divalent linking group selected from thegroup consisting of a single bond, -alkylene-, -alkenylene-,-alkynylene-, —O—, —S—, —CO—, —NR—, —SO₂— and any combinations thereof.R is a hydrogen atom or C1-30 alkyl group. L⁵³ is desirably a divalentlinking group selected from the group consisting of —O—, —S—, —CO—,—NR—, —SO₂— and any combinations thereof. R is desirably a hydrogen atomor C1-20 alkyl group, preferably a hydrogen atom or C1-15 alkyl group,and more preferably a hydrogen atom or C1-12 alkyl group.

The number of the carbon atoms included in the alkylene group isdesirably from 1 to 40, preferably from 1 to 30, more preferably from 1to 15 and much more preferably from 1 to 12.

The number of the carbon atoms included in the alkenylene group isdesirably from 2 to 40, preferably from 2 to 30, more preferably from 2to 15 and much more preferably from 2 to 12.

The specific example of L⁵³ are shown below. In the following examples,the left end of an exemplified group is bonded to Cy⁵¹ and the right endis bonded to Cy⁵².

L²⁰: single bond

L²¹: —S—

L²²: —NH—

L²³: —NH—SO₂—NH—

L²⁴: —NH—CO—NH—

L²⁵: —SO₂—

L²⁶: —O—NH—

L²⁷: —C≡C—

L²⁸: —CH═CH—S—

L²⁹: —CH₂—O—

L³⁰: —N(CH₃)—

L³¹: —CO—O—

In the Formula (V-a), n is an integer from 2 to 12, desirably from 2 to9, preferably from 2 to 6, more preferably 2, 3 or 4, and much morepreferably 3 or 4.

In the Formula (V-a), Cy⁵² is an n-valent cyclic group. Cy⁵² isdesirably an n-valent aromatic hydrocarbon group or n-valentheterocyclic group.

The examples of the aromatic hydrocarbon ring included in the aromatichydrocarbon group denoted by Cy⁵² include a benzene ring, indene ring,naphthalene ring, fluorine ring, phenanthrene ring, anthracene ring andpyrene ring. Among them, a benzene ring and naphthalene ring arepreferred and a benzene ring is more preferred.

The aromatic hydrocarbon group denoted by Cy⁵² may have at least onesubstituent. The examples of the substituent include an aliphatic group,aromatic hydrocarbon group, heterocyclic group, halogen atom, alkoxygroup (e.g., methoxy, ethoxy, methoxy-ethoxy), aryloxy group (e.g.,phenoxy), arylazo group (e.g., phenylazo), alkylthio group (e.g.,methylthio, ethylthio, propylthio), alkylamino group (e.g., methylamino,propylamino), arylamino group (e.g., phenylamino), acyl group (e.g.,acetyl, propanoyl, octanoyl, benzoyl), acyloxy group (e.g., acetoxy,pivaloyloxy, benzoyloxy), hydroxy, mercapto, amino, carboxy, sulfo,carbamoyl, sulfamoyl and ureido.

The hetero ring included in the divalent heterocyclic group denoted byCy⁵² is desirably five-, six- or seven-membered, preferably five- orsix-membered, and more preferably six-membered. The hetero atomconstituting the hetero ring is desirably nitrogen, oxygen or sulfur.The hetero ring desirably has aromaticity. Aromatic hetero rings areusually unsaturated rings and desirably has maximum double bondings. Theexamples of the hetero ring include a furan ring, thiophene ring,pyrrole ring, pyrroline ring, pyrrolizine ring, oxazole ring, isoxazolering, thiazole ring, isothiazole ring, imidazole ring, imidazoline ring,imidazolidine ring, pyrazole ring, pyrazoline ring, pyrazolidine ring,triazole ring, furazan ring, tetrazole ring, pyrane ring, thiine ring,pyridine ring, piperidine ring, oxazine ring, morpholine ring, thiazinering, pyridazine ring, pyrimidine ring, pyrazine ring, piperazine ringand triazine ring. Among them, triazine ring is preferred and1,3,5-triazine ring is more preferred.

Although the hetero rings may be condensed with other hetero rings,aliphatic rings or aryl rings, monocyclic hetero rings are preferred.

The specific examples of Cy⁵² are shown below.

The alignment promoter is a compound comprising the aforementionedhydrophobic group (Hb), the linking group (L⁵²) and the group (Bu)showing an excluded volume effect. There is no specific limitation onthe combinations thereof.

The specific examples of the alignment promoters denoted by the Formula(V) are shown below.

[Alignment Layer]

For aligning rod-like liquid-crystal molecules so as to prepare theoptically anisotropic layers respectively, alignment layers may be used.There have been provided alignment layers formed of various materials byvarious methods such as subjecting a film made of an organic compound(preferably a polymer) to a rubbing treatment, obliquely depositing aninorganic compound, forming a layer having microgrooves, or accumulatingan organic compound (e.g., ω-trichosanic acid, dioctadecylmethylammoniumchloride, methyl stearate) by Langmuir-Blodgett method (LB film).Alignment layers having an alignment effect under an electric ormagnetic field or irradiation are also known. According to the presentinvention, the alignment layer prepared by subjecting a film of apolymer to a rubbing treatment is desirable as an alignment layer forthe lower layer. The rubbing treatment is performed by rubbing thesurface of the polymer layer in a direction several times with paper ora cloth. In general, rod-like liquid-crystal molecules in a layer formedon an alignment layer are aligned in a direction depending on therubbing direction of the alignment layer. Thus, it is possible tocontrol the alignment direction of the rod-like liquid-crystal moleculesby adjusting the rubbing direction of the alignment layer. Whenhomogeneous alignment layers, which are capable of aligningliquid-crystal molecules in a homogeneous alignment state, are employedin the present invention for the first and second optically anisotropiclayer, preferably, one of them has a rubbing axis inclined +30 degreesrelative to the longitudinal direction and the other has a rubbing axisinclined −30 degrees relative to the longitudinal direction.

Materials for preparing the alignment layer are not specifically limitedand may be selected depending on desired liquid-crystal alignment(especially a mean tilt angle). In order to align the liquid-crystalmolecules homogeneously, a polymer used in preparing an alignment layeris desirably selected so as not to lower the surface energy of thealignment layer. Specific examples of the polymers are described invarious literatures relating to liquid-crystal cells or opticalcompensation sheets. For improving adhesion between the liquid-crystalcompound and the transparent substrate, the alignment layer is desirablyformed of a polymer having a polymerizable group. The polymerizablegroup may be introduced to the polymer as a portion in a side chain of arepeating unit constituting the polymer or as a cyclic substituent groupof the polymer. The polymers capable of forming chemical bonds withliquid-crystal molecules at the interface between the alignment layerand the lower layer are desirably used, and alignment layers formed ofsuch polymers are described in JPA No. 1997-152509.

The thickness of the alignment layer is preferably 0.01 to 5 micrometers, and more preferably 0.05 to 1 micro meters.

For preparing a first optically anisotropic layer, the alignment layermay be formed on a temporary substrate and an optically anisotropiclayer may be formed by aligning the liquid-crystal compound on thealignment layer and then transferred onto a transparent substrate suchas a plastic film. The liquid-crystal compound can maintain an alignmentwithout any alignment layer after being fixed in the alignment.Additionally, for preparing a second optically anisotropic layer on afirst optically anisotropic layer, a surface of the first opticallyanisotropic layer may be subjected to a rubbing treatment directly and acomposition comprising a liquid-crystal compound may be applied to therubbed surface to prepare the second optically anisotropic layer. Thus,the retarder of the present invention doesn't necessarily comprise analignment layer.

[Substrate]

The substrate is transparent desirably. In particular, the substratepreferably has a transmittance of 80% or more. The substrate with lowwave length dispersion is used desirably. In particular, the substratehas an Re400/Re700 ratio of less than 1.2 desirably. The substrate has asmall optical anisotropy desirably. In particular, the substratedesirably has an in-plane retardation (Re) of 20 nm or less, and morepreferably 10 nm or less. The long substrate has the form of a roll or arectangular sheet. Preferably, the first and second layers are preparedon a substrate in the form of a roll, thereby forming a multilayer roll,and then the multilayer roll is cut into a desirable size.

Materials for the substrate include, but not specifically limited to,glass plates or polymer films, among which polymer films are preferredto obtain light-weight thin-layer products. Examples of polymers includecellulose esters, polycarbonates, polysulfones, polyether sulfones,polyacrylates and polymethacrylates, preferably cellulose esters, morepreferably acetyl cellulose, most preferably triacetyl cellulose. Thepolymer films are preferably formed by solvent casting. The thickness ofthe transparent substrate is preferably 20 to 500 micro meters, morepreferably 50 to 200 micro meters. The transparent substrate may besubjected to a surface treatment (e.g., glow discharge treatment, coronadischarge treatment, UV treatment, flame treatment) to improve adhesionbetween the transparent substrate and the overlying layer (an adhesivelayer, orthogonal alignment layer or optically anisotropic layer). Anadhesive layer (undercoat layer) may be provided on the transparentsubstrate.

[Circular Polarizer Plate]

The retarder of the present invention is most advantageous when it isapplied to a quarter wave plate used for reflective-type liquid-crystaldisplay devices, write pickups for optical disks, or anti-reflectivefilms. The quarter wave plate is generally configured as a circularpolarizer plate as being combined with a linear polarizer film.Therefore the quarter wave plate configured as a circular polarizerplate as being combined with a linear polarizer film can readily beincorporated into devices such as having functions of reflective-type,liquid-crystal display devices. Known types of the linear polarizer filminclude iodine-containing polarizer film, dye-containing polarizer filmusing dichroic dye, and poly-ene containing polarizer film. Theiodine-containing polarizer film and dye-containing polarizer film aregenerally manufactured using poly(vinyl alcohol)-base films.

The present invention employs a linear polarizer film having atransparent axis inclined substantially at +45 degrees or −45 degreesrelative to the longitudinal direction of the film (simply referred toas “45° linear polarizer film”). Since usually a linear polarizer filmcomposed of a stretched film has a transparent axis substantiallyparallel to a stretching direction, a 45° linear polarizer film can beprepared by stretching a film in a direction inclined at 45 degreesrelative to the longitudinal direction of the film.

[45° Polarizer Film]

FIGS. 3 and 4 show schematic plan views of an exemplary process ofoblique stretching of a polymer film.

The stretching process comprises a step of introducing a source filmindicated by range (a) along the direction of arrow (i); a step ofeffecting width-wise-direction stretching as indicated by range (b); anda step of feeding the stretched film indicated by range (c) to the nextprocess step, or to the direction of arrow (ii). It is to be understoodthat any notation of “stretching step” hereinafter indicates the entireprocess of executing the stretching method including the steps (a) to(c).

The film is continuously fed from direction (i), and is held by aholding means located on the left edge side as viewed from the upstreamat point B1 for the first time. At this point of time, the opposite edgeof the film is not held yet, so that there is still no tensile forceexerted in the width-wise direction. Point B1 is therefore notunderstood as a substantial starting point for holding in the stretchingprocess.

In the stretching process, the true substantial hold-start point isdefined by a point where the both edges of the film are held for thefirst time. The substantial hold-start point is expressed by a pair ofpoints comprising hold-start point A1 on the further downstream side,and point C1 which falls on the intersection of the line drawn frompoint A1 substantially normal to the center line 11 (FIG. 3) or 21 (FIG.4) of the film on the feeding side with a locus 13 (FIG. 3) or 23 (FIG.4) of the opposite holding means.

When the holding means on both sides travel at a constant speed fromthese start points, point A1 moves to points A2, A3, . . . , An as beingscaled by a unit time, and point C1 similarly moves to points C2, C3, .. . , Cn. That is, a line connecting the points An and Cn, where thereferential holding means pass at the same time, expresses thestretching direction at that point of time.

In the stretching process, An gradually falls behind Cn as shown inFIGS. 3 and 4, and this makes the stretching direction incline away fromthe direction normal to the travel direction. A point where the holdingis substantially released in the stretching process is defined by a pairof points comprising point Cx where the film is released from theholding means on the upstream side, and point Ay which falls on theintersection of the line drawn from point Cx substantially normal to thecenter line 12 (FIG. 3) or 22 (FIG. 4) of the film to be sent to thenext process with a locus 14 (FIG. 3) or 24 (FIG. 4) of the oppositeholding means.

Final angle of the stretching direction of the film is determined by aratio of path difference Ay-Ax (i.e., |L1-L2|) of the left and rightholding means at the substantial end point (substantial hold-releasepoint) of the stretching process and distance W (distance between Cx andAy) of the substantial hold-release point. Therefore, an angle ofinclination θ of the stretching direction away from the sendingdirection towards the next process is defined as an angle satisfying theequations below:tan θ=W/(Ay−Ax), ortan θ=W/|L1−L2|

Although the upper film end shown in FIGS. 3 and 4 is held after passingpoint Ay until point 18 (FIG. 3) or 28 (FIG. 4) is reached but the lowerend of the film is not held, so that, there is no more tensile forcenewly generated. Points 18 and 28 are therefore not understood assubstantial hold-release points in the present invention.

As described in the above, the substantial hold-start points reside onboth edges of the film in this stretching process are not mere pointswhere engagement into the left and right holding means take place.According to more strict expression of the above definition, the twoabove substantial hold-start points in the stretching process can bedefined as a pair of two holding points which reside most upstream amongpairs of the holding points respectively allowing that a line connectingeither left or right holding point with the other holding point crossesapproximately normal to the center line of the film to be sent to theprocess in which the film is held.

Similarly, the two above substantial hold-release points in thestretching process can more strictly be defined as a pair of two holdingpoints which reside most downstream among pairs of the holding pointsrespectively allowing that a line connecting either left or rightholding point with the other holding point crosses approximately normalto the center line of the film to be sent to the next process.

It is to be understood that “approximately normal” stated herein meansthat the center line of the film and a line connecting the left andright substantial hold-start points or substantial hold-release pointscross at 90±0.5 degrees.

For the case where the difference in the left and right paths in theabove stretching process is created using a tenter-type stretchingmachine, a large difference may occur between the point of engagementinto the holding means and the substantial hold-start points, or betweenthe point of release from the holding means and the substantialhold-release points, due to mechanical restrictions such as rail length.Purpose of the stretching process can, however, be achieved if theprocess between the substantial hold-start points and the substantialhold-release points satisfies the relation of (1) |L2−L|>0.4 W.

Angle of inclination of the orientation axis of the stretched filmobtained in the above process can be controlled and adjusted based onthe ratio of width W of the exit from step (c) and path difference|L1−L2 | between two substantial holding means on the left and right.

It is often required for polarizer plates and wave retarder films tohave a film oriented at 45° relative to the longitudinal directionsthereof. In order to achieve an angle of orientation close to 45degrees, it is preferable to satisfy the relation of (2) 0.9W<|L1−L2|<1.1 W, is more preferable to satisfy the relation of (3) 0.97W<|L1−L2|<1.03 W.

Specific configuration of the stretching process can arbitrarily bedesigned as shown in FIGS. 3 to 8 considering facility costs andproductivity, so far as the relation (1) is satisfied.

An arbitrary value can be adopted for the angle between the film feedingdirection (i) into the stretching process and the film sending direction(ii) towards the next process step, where smaller angle is better inview of minimizing the total installation area of the facility includingthe process steps before and after the stretching process, which ispreferably 3 degrees or less, and more preferably 0.5 degrees or less.These values can be attained by exemplary configurations shown in FIGS.3 and 6.

In such methods where the film traveling direction does notsubstantially change, it is difficult to obtain an angle of orientationof 45 degrees, suitable for polarizer plates and wave retarder films,relative to the longitudinal directions thereof solely by widening thedistance between the holding means. One possible process is such ashaving a step of once stretching the film, and then shrinking it tothereby increase |L1−L2|, as shown in FIG. 3.

Stretching ratio is preferably 1.1 to 10.0 times, more preferably 2 to10 times, and shrinkage ratio thereafter is preferably 10% or more. Itis also preferable, as shown in FIG. 6, to repeatstretching-and-shrinkage a plural number of times because |L1−L2| can beincreased.

In view of minimizing the facility costs of the stretching process, asmaller number and a smaller angle of the bend in the loci of theholding means are better. From this viewpoint, as shown in FIGS. 4, 5and 7, the traveling direction of the film is preferably bent whilekeeping the film held at both edges thereof, so that the travelingdirection of the film at the exit of the process during which both edgesof the film are held is inclined at 20 to 70 degrees relative to thesubstantial stretching direction of the film.

So-called tenter machines as shown in FIGS. 3 to 7 are preferably usedas an apparatus for stretching the film while keeping the both edgesthereof held under tension during the stretching. Besides theconventional two-dimensional tenters, it is also allowable to use atenter as shown in FIG. 8, in which a spiral path difference generatesbetween the holding means on both edges.

Most tenter stretchers are configured so that a chain having clips fixedthereto is guided along the rails, where any laterally-unbalancedstretching process as described in the above may shift the ends of therails at the entrance and exit of the process as shown in FIGS. 3 and 4,and this may prevent simultaneous engagement or release on both edges.The substantial lengths of path L1, L2 in this case are not expressedmerely by a distance between the points of engagement and release but,strictly as described in the above, a length of path over which bothedges of the film are held by the holding means.

Because any difference in the traveling speed on both edges of the filmat the exit of the stretching process is causative of wrinkle or gather,travel speeds of the holding means on both lateral sides of the filmmust be substantially equivalent. Allowable difference in the speed ispreferably 1% or less, more preferably 0.5% or less, and still morepreferably 0.05% or less. The speeds stated herein refers to lengths ofloci along which the individual left and right holding means advance perminute. General tenter stretchers have variation in the speed in theorder of second or less depending on periodicity of sprocket teeth orfrequency of a drive motor, which often amounts several percents. Thisis, however, not included in the difference in speed in the context ofthe present invention.

The film tends to cause wrinkle or gather as the path difference betweenthe left-hand side and right-hand side increases. To solve this problem,it is preferable to carry out the stretching while keeping thesupportability of the polymer film and keeping the volatile fraction at5% or above, and then allow the film to shrink to thereby lower thevolatile fraction. Possible methods for allowing the film to containvolatile components are such as casting the film so as to take up thesolvent or water, such as subjecting the film to immersion, coating orspraying with the solvent or water before the stretching, and such ascoating the solvent or water during the stretching. Because hydrophilicpolymer films such as polyvinyl alcohol films can usually contain waterunder a high-temperature, high-humidity atmosphere, volatile componentscan be included in such films by stretching the films after beingconditioned under a high-humidity atmosphere, or by stretching the filmunder a high-humidity atmosphere. Any other methods are available so faras they can adjust contents of volatile components in the polymer filmto as high as 5% or above.

Preferable volatile fraction may differ by species of the polymer film,and can be maximized so far as the supportability of the polymer film isretained at a desirable level. The volatile fraction is preferablywithin a range from 10 to 100% for polyvinyl alcohol, and 10 to 200% forcellulose acylate. Shrinkage of the stretched polymer film can beeffected in either timing of during or after the stretching. While ameans for shrinking the film is typified by raising of the temperatureso as to remove the volatile contents, any other methods may beallowable so far as they can successfully shrink the film.

As has been described in the above, a preferable embodiment of thestretching process satisfies the conditions that:

(i) the film is stretched by at least 1.1 to 20.0 times in thewidth-wise direction thereof;

(ii) the difference in the longitudinal traveling speed between theholding means on both edges of the film is 1% or less;

(iii) the traveling direction of the film is bent while both edgesthereof are held, so that the traveling direction at the exit of theprocess is inclined at 20 to 70 degrees relative to the substantialstretching direction; and

(iv) the film is stretched while keeping the supportability of thepolymer film and a keeping the volatile fraction contained therein at 5%or above, and then shrunk to thereby lower the volatile fraction.

It is often necessary for the rails used for limiting the loci of theholding means in the present invention to have a large bending ratio.For the purpose of avoiding mutual interference between the holdingmeans due to a sharp bending, or local stress concentration, the railsare preferably designed so that the holding means can trace arc loci.

There are no special limitations on the polymer film to be stretched inthe present invention, so that films comprising any appropriatethermoplastic polymer are available. Examples of the polymer includePVA, polycarbonate, cellulose acylate and polysulfone.

While thickness of the film before stretching is not specificallylimited, it is preferably 1 micro meters to 1 mm from the viewpoints ofstability in holding of the film and uniformity in the stretching, wherethe thickness is more preferably 20 to 200 micro meters.

The stretched films prepared by the above mentioned process may be usedin various applications, desirably used as a polarizer film or aretarder film, from the viewpoint of their features such that theirorientation axes are inclined relative to the longitudinal direction. Inparticular, any polarizer films having the orientation axis inclined at40 to 50 degrees relative to the longitudinal direction are preferablyused as a polarizer plate for LCD. More preferable angle of inclinationfalls within a range from 44 to 46 degrees.

When the above-described process is applied to fabrication of thepolarizer film, PVA film is preferably used as the polymer film. WhilePVA is generally obtained by saponifying poly(vinyl acetate), the PVAmay also contain any component co-polymerizable with vinyl acetate, suchas unsaturated carboxylic acid, unsaturated sulfonic acid, olefins andvinyl ethers. It is also allowable to use modified PVA containingacetoacetyl group, sulfonic acid group, carboxyl group, oxyalkylenegroup and the like.

While there are no special limitations on the degree of saponificationof PVA, it is preferably adjusted within a range from 80 to 100 mol % inview of solubility and so forth, and more preferably from 90 to 100 mol%. While there are no special limitations also on the degree ofpolymerization of PVA, it is preferably adjusted within a range from1,000 to 10,000, and more preferably 1,500 to 5,000.

By dyeing the PVA film, the polarizer film may be prepared and thedyeing process may be proceeded by adsorption from vapor phase or liquidphase. In one exemplary process for the liquid phase adsorption usingiodine, the absorption is carried out by immersing a PVA film into anaqueous iodine-potassium iodide solution. Contents of iodine andpotassium iodide are preferably 0.1 to 20 g/L and 1 to 100 g/L,respectively, and a weight ratio of iodine and potassium iodidepreferably falls within a range from 1 to 100. Time for the dyeing ispreferably 30 to 5,000 seconds, and the solution temperature ispreferably within a range from 5 to 50° C. The dyeing method is not onlylimited to immersion, but allows arbitrary means such as coating orspraying of iodine or a dye solution. The dyeing process may precede orfollow the stretching process, where the dyeing before the stretching isparticularly advantageous because the film is appropriately swollen andto thereby facilitate the stretching. Besides iodine, it is alsopreferable to use dichroic dyes for the dyeing. Specific examples of thedichroic dyes include dye compounds such as azo dyes, stilbene dyes,pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes,thiazine dyes and anthraquinone dyes. Although those soluble in waterare preferable, not limitative thereto. It is also preferable that thesedichroic dyes have introduced therein a hydrophilic substitutive groupsuch as sulfonic acid group, amino group and hydroxyl group. Specificexamples of the dichroic dyes include C.I. Direct Yellow 12, C.I. DirectOrange 39, C.I. Direct Orange 72, C.I. Direct Red 39, C.I. Direct Red79, C.I. Direct Red 81, C.I. Direct Red 83, C.I. Direct Red 89, C.I.Direct Violet 48, C.I. Direct Blue 67, C.I. Direct Blue 90, C.I. DirectGreen 59, C.I. Acid Red 37, and those described in Japanese Laid-OpenPatent Publication Nos. 1-161202, 1-172906, 1-172907, 1-183602,1-248105, 1-265205 and 7-261024. These dichroic molecules are used in aform of free acid, alkali metal salt, ammonium salt or salts of amines.Mixing of two or more of these dichroic molecules successfully producespolarizers having various hues. Compounds (dyes) or mixtures of variousdichroic molecules designed to exhibit black color when contained inpolarizer elements or polarizer plates and when the transparent axesthereof are crossed normal to with each other are preferable, becausethey are excellent in single-plate transmissivity and in polarizationratio.

In the stretching of PVA for fabricating the polarizer film, it ispreferable to add an additive for crosslinking to PVA. In particular forthe case where the oblique stretching process of the present inventionis adopted, direction of orientation of PVA may be misaligned due totension in the process unless the PVA film is sufficiently cured at theexit of the stretching process, so that it is preferable to allow thecrosslinking agent to be contained in the PVA film by immersion orcoating of a solution of such crosslinking agent before or during thestretching process. The crosslinking agents disclosed in the U.S.Reissue Pat. No. 232897 are available for the present invention, whereboric acids are most preferably used.

The above-mentioned stretching process is also desirably applicable tofabrication of so-called polyvinylene-base polarizer film, wherepolarizing function of which is ascribable to conjugated double bonds inthe poly-ene structure obtained by dehydrating and dechlorinating PVAand poly (vinyl chloride).

The polarizer film fabricated by the above-mentioned oblique stretchingprocess can be configured without any modification as a polarizer plateand used as the retarder of the present invention, but it is morepreferably used as the polarizer plate after being bonded with aprotective film on one side or both sides thereof. There are no specificlimitations on the species of the protective film, and availableexamples thereof include cellulose esters such as cellulose acetate,cellulose acetate butylate and cellulose propionate; polycarbonate;polyolefin; polystyrene; and polyester. Retardation value of theprotective film exceeding a certain value is, however, not desirablesince oblique misalignment between the transparent axis and theorientation axis of the protective film results in conversion of linearpolarization into circular polarization. The retardation value of theprotective film is preferably small, which is typified by 10 nm or lessat 632.8 nm, and more preferably 5 nm or less. Cellulose triacetate isparticularly preferable as a polymer for composing the protective filmhaving such a low level of retardation value. Polyolefins such as ZEONEXand ZEONOR (trade names, products of ZEON Corporation, JAPAN), and ARTON(trade name, product of JSR Corporation, JAPAN). Other availableexamples thereof include non-birefringent optical resin materialsdescribed in Japanese Laid-Open Patent Publication Nos. 8-110402 and11-293116.

Although an adhesive possibly used between the polarizer film and theprotective layer is not specifically limited, PVA resins (including PVAsmodified with acetoacetyl group, sulfonic acid group, carboxyl group,oxyalkylene group, etc.) and aqueous boron compound solution areavailable, and among others, the PVA resins are preferable. Thickness ofa dried layer of the adhesive preferably falls within a range from 0.01to 10 micro meters, and more preferably 0.05 to 5 micro meters.

An exemplary conventional punching pattern of the polarizer plates, andan exemplary inventive punching pattern of the polarizer plates areshown in FIGS. 9 and 10, respectively. The conventional polarizingplates have, as shown in FIG. 9, an absorption axis 71, that is thestretching axis, parallel to the longitudinal direction 72. On the otherhand, the polarizer plates of the present invention have, as shown inFIG. 10, an absorption axis 81 of polarization, that is the stretchingaxis, inclined at 45 degrees relative to the longitudinal direction 82.Thus, it is not necessary to obliquely punch out the film in thepunching process. This is also advantageous in that, as is obvious fromFIG. 10, the polarizer plates can be produced by slitting along thelongitudinal direction, rather than by punching, because the cuttingline for producing the polarizer plates prepared by the above mentionedprocess straightly extends along the longitudinal direction, and thisensures excellence in the productivity.

The linear polarizer plate used in the present invention preferably hasa large transmissivity and a large degree of polarization in view ofraising contrast of the liquid-crystal display device. Thetransmissivity is preferably 30% or more at 550 nm, and more preferably40% or more. The degree of polarization is preferably 95.0% or more at550 nm, more preferably 99% or more, and still more preferably 99.9% ormore. The linear polarizer film generally has protective films on bothsurfaces thereof. In the present invention, the retarder of the presentinvention can be functioned as the protective film on one side of thelinear polarizer film. For the case where the circular polarizer plateis fabricated using the 45° polarizer film, right and left circularpolarizer plates can readily be fabricated in a selective manner bychanging the way of stacking.

[Configuration of Circular Polarizer Plate]

FIG. 11 shows a conceptual drawing of one embodiment of the circularpolarizer plate of the present invention.

The circular polarizer plate shown in FIG. 11 is configured so as tostack a 45° polarizer film P and a protective film G on the retarder ofthe present invention. The retarder comprises an optically anisotropiclayers A and B (shown as a single layer in FIG. 11), and a transparentsubstrate S. The retarder is stacked with the 45° polarizer film P, sothat the surface opposite to that having the optically anisotropiclayers A and B formed thereon is towards the 45° polarizer film P. Inthis configuration, the retarder also functions as a protective film forthe 45° polarizer film P. FIG. 11 also shows interrelations among thelongitudinal direction s of the transparent substrate S, the slow axes aand b of the optically anisotropic layers A and B, and the transparentaxis p of the 45° polarizer film P.

In incorporation of the circular polarizer plate shown in FIG. 11 intodisplay devices, the protective film P side is directed to the displaysurface side (an arrow in the drawing indicates the direction ofviewing). Circular polarization obtained by the configuration shown inFIG. 11 is a right circular polarized light. Light comes from thedirection indicated by the arrow in FIG. 11 sequentially passes throughthe polarizer film P and optically anisotropic layers A and B, and goesout as a right circular polarized light.

Another exemplary constitution of the circular polarizer plate of thepresent invention is shown in FIG. 12. The circular polarizer plateshown in FIG. 12 has a configuration in which positions of theprotective film G and retarder previously shown in FIG. 11 wereexchanged, where protective film G, 45° polarizer film P, transparentsubstrate S and optically anisotropic layers A and B are stacked in thisorder. The configured circular polarizer plate can generate a leftcircular polarized light.

As is obvious from the above, a right circular polarized light and leftcircular polarized light can selectively be obtained only by changingthe top and bottom of the stacking when the protective film G andretarder are bonded to the 45° polarizer film P.

For the case where the protective film is used besides the transparentsubstrate, the protective film is preferably composed of a celluloseester film having a high optical isotropy, where triacetyl cellulosefilm is particularly preferable.

In the present specification, the term of “broadband quarter wave plate”is used for any quarter wave plate having values of {(retardationvalue/(wavelength)} measured at 450 nm, 550 nm and 650 nm fall within arange from 0.2 to 0.3. The value of retardation value/wavelength ispreferably within a range from 0.21 to 0.29, more preferably 0.22 to0.28, still more preferably 0.23 to 0.27, and most preferably from 0.24to 0.26.

EXAMPLES

The following paragraphs will further detail the present inventionreferring to specific examples. Any materials, reagents, ratio of useand operations may properly be modified without departing form thespirit of the present invention. It is therefore be understood that thescope of the present invention is by no means limited by the Examplesbelow.

Example 1

An optically-isotropic triacetyl cellulose, which has an acetylationdegree of 60.9%, film in the form of 80 micro meters in thickness, 680mm in width and 500 m in length was used as a transparent substrate.Both surfaces of the transparent substrate were saponified. A coatingsolution having a composition described below for an alignment layer (apolymer of the structural formula shown below) was continuously appliedto the surface of the transparent substrate and dried to form a layerhaving a thickness of 1 micro meter. The, a rubbing treatment wascontinuously performed to a surface of the layer in a direction at +30degrees relative to the longitudinal direction of the transparentsubstrate to form an alignment layer.

Composition of coating solution for alignment layer  10 weight partsModified polyvinyl alcohol below

Water 371 weight parts Methanol 119 weight parts Glutaraldehyde  0.5weight parts

A coating solution of the composition below was continuously applied tothe rubbed surface of the alignment layer with a bar coater, dried,heated (matured in alignment) and further irradiated with UV rays toform an optically anisotropic layer (A), in other words a firstoptically anisotropic layer, having a thickness of 2.0 micro meters. Theoptically anisotropic layer (A) had a slow axis in a direction at +30degrees relative to the longitudinal direction of the transparentsubstrate. The retardation value at 550 nm was 265 nm.

Composition of the coating solution for the optically anisotropic layer(A) Rod-like liquid-crystal compound No. I-2 38.1 wt % denoted by theFormula (I) Sensitizer (1) below 0.38 wt %

Photo-polymerization initiator (1) below 1.14 wt %

Additive (1) below 0.38 wt %

Glutaraldehyde 0.04 wt % Methyl ethyl ketone 60.00 wt % 

A rubbing treatment was continuously performed to a surface of the layer(A) in a direction at 60 degrees relative to the slow axis of the layer(A) and at −30 degrees relative to longitudinal direction of thetransparent substrate. A coating solution of the composition below wascontinuously applied to the rubbed surface of the layer (A) with a barcoater, and dried and heated (matured in alignment), and furtherirradiated with UV rays to form an optically anisotropic layer (B)having a thickness of 1.0 micro meters. The retardation value at 550 nmwas 135 nm.

Composition of the coating solution for the optically anisotropic layer(B) The rod-like liquid-crystal compound No. I-2 38.4 wt % denoted bythe Formula (I) The sensitizer (1) 0.38 wt % The photo-polymerizationinitiator (1) 1.15 wt % Compound No. V-(27) denoted by the Formula (V)0.06 wt % Methyl ethyl ketone 60.0 wt %

Example 2

The retarder was prepared in the same manner as Example 1 except that arod-like liquid-crystal compound No. I-4 was used for preparing theoptically anisotropic layers (A) and (B) in the place of the rod-likeliquid-crystal compound No. I-2. The resultant optically anisotropiclayer (A) was found to have an average retardation value at 550 nm of251 nm, and the resultant optically anisotropic layer (B) was found tohave an average retardation value at 550 nm of 135 nm.

Example 3

The retarder was prepared in the same manner as Example 1 except that arod-like liquid-crystal compound No. I-15 was used for forming theoptically anisotropic layers (A) and (B) in the place of the rod-likeliquid-crystal compound No. I-2. The resultant optically anisotropiclayer (A) was found to have an average retardation value at 550 nm of250 nm, and the resultant optically anisotropic layer (B) was found tohave an average retardation value at 550 nm of 135 nm.

Comparative Example 1

A trail of fabricating a retarder by replacing the rod-likeliquid-crystal compound No. I-2 used for preparing the opticallyanisotropic layers (A) and (B) in Example 1 with a comparative rod-likeliquid-crystal compound (1) shown below resulted in failure, sinceinsoluble matter was generated in the coating solutions. The compositionof the coating solutions was then altered as shown below, and except forthis alteration, the retarder was fabricated similarly to as describedin Example 1 or 2.

Composition of Coating Solution for Optically anisotropic Layer (A)Comparative rod-like liquid-crystal compound (1) 14.5 wt %

The sensitizer (1) 0.14 wt % The photo-polymerization initiator (1) 0.43wt % The additive (1) 0.14 wt % Glutaraldehyde 0.02 wt % Methyl ethylketone 84.8 wt % Composition of Coating Solution for Opticallyanisotropic Layer (B) The comparative rod-like liquid-crystal compound(1) 14.5 wt % The sensitizer (1) 0.14 wt % The photo-polymerizationinitiator (1) 0.43 wt % The compound V-(27) denoted by the Formula (V)0.02 wt % Methyl ethyl ketone 84.8 wt %

Example 4

A PVA film was immersed in an aqueous solution containing 2.0 g/L iodineand 4.0 g/L potassium at 25 degrees Celsius for 240 seconds andsubsequently in an aqueous solution of 10 g/L boric acid at 25 degreesCelsius for 60 seconds. The PVA film was introduced into a tenterstretcher same as that shown in FIG. 4 and stretched by 5.3 times. Whilethe tenter was bent far from the stretching direction in the same manneras shown FIG. 4 and the tenter width was kept constant, the PVA film wasdried in an atmosphere of 80 degrees Celsius, contracted and put out ofthe tenter. The PVA film contained 31% moisture before stretching and1.5% after drying respectively.

The difference in traveling speed between the left and an right tenterclips was less than 0.05%; and an angle between the center line of thePVA film to be introduced into the stretcher and the center line of thePVA film to be sent to a next step was 46°. The used tenter stretcherhad |L1−L2| of 0.7 m and W of 0.7 m, that is, satisfying a relation of|L1−L2 |=W. “Ax−Cx”, at the exit of the tenter stretcher is inclined at45 relative to the center line 22 of the PVA film to be sent to a nextstep. Neither winkle nor deformation of the PVA film was found at theexit of the tenter stretcher.

A commercially available cellulose acetate film (“FUJITAC” whoseretardation was 3.0 nm, FUJI PHOTO FILM Co., LTD.) was subjected tosaponification treatment, and then the film was laminated on the surfaceof the obtained stretched PVA film with an aqueous solution of 3% PVA(PVA-117H, KRARAY CO., LTD.) as an adhesive, and dried at 80 degreesCelsius. Then, a linear polarizer plate having a working width of 650 mmwas obtained.

The obtained linear polarizer plate had an absorption axis in adirection inclined at 45 degrees relative to the longitudinal direction.The polarizer plate had a transmittance of 43.7% and a polarizationdegree of 99.97%. The polarizer plate was cut into a piece having adimension of 310 mm×233 mm in the same manner as that shown in FIG. 10.Thus, the polarizer plate having the dimension and an absorption axis ina direction inclined at 45 degrees relative to the side at an areaefficiency of 91.5%.

Next, as shown in FIG. 13, a circular polarizer plate 92 was prepared bylaminating the retarder 96 prepared in Example 1 on one surface of theiodine-based linear polarizer film 91 prepared in the above, and bylaminating on the opposite surface a saponified antidazzleantireflective film 97. Still other polarizer plates 93 to 95 weresimilarly prepared except that the retarders prepared in Examples 2, 3and Comparative Example 1 were used respectively in place of theretarder 96 respectively. In all process for preparing these circularpolarizer plates, the linear polarizer film and retarder were laminatedso as to conform the longitudinal directions each other.

Each of thus obtained circular polarizer plates 92 to 95 was irradiatedwith light (450 nm, 550 nm and 650 nm) from the antidazzleantireflective film 97 side, and phase difference (retardation value:Re) of the transmitted light was measured at arbitrary 20 points whichfall within an area of 650 mm wide and 1,000 mm long, and the ranges ofvariation were expressed by the maximum values and minimum values. Theretarder before being incorporated in the circular polarizer plate wasalso observed under a polarizing microscope (×100), and number ofalignment defects (average of results from 10 visual fields) werecounted. Results were summarized in the table below.

TABLE 1 Circular polarizer Retarder Re Re Re Number of plate No. used(450 nm) (550 nm) (650 nm) Defects 92 Example 1 110-113 nm 133-137 nm142-146 nm 1 93 Example 2 109-114 nm 132-138 nm 141-147 nm 2 94 Example3 110-114 nm 133-137 nm 141-147 nm 1 95 Comparative 104-118 nm 127-143nm 136-152 nm 10 or more Example 1 Ideal value 112.5 nm 137.5 nm 157.5nm 0

As shown in Table 1, according to the present invention, it issuccessful in preparing circular polarizer plates less in in-planevariation, less in defects, and excellent in stability.

Example 5

(Preparation of Reflective-Type, Liquid-Crystal Display Device)

A polarizer plate and a retarder were removed from a commercialreflective-type, liquid-crystal display device (“Color Zaurus”, productof SHARP Corporation, Japan), and the circular polarizer plate 92 to 95were respectively attached instead.

Evaluated by visual obseravation, it was found that all of thesecircular polarizer plates 92 to 95 resulted in neutral gray display ineither of white display, black display and half tone display, withoutdeveloping color.

Next, contrast ratio based on reflective luminance was measured using aviewing angle measuring instrument (EZcontrast160D, product of Eldim SA,France). The contrast ratios measured at the front face through thecircular polarizer plates comprising the retarders fabricated inExamples 2, 3 and 4 were found to be 10, 9 and 10, respectively, whichwere practical enough. On the other hand, contrast ratio measured at thefront face through the circular polarizer comprising the retarderfabricated in Comparative Example 1 was found to show a large in-planevariation ranging from 6 to 10.

INDUSTRIAL AVAILABILITY

According to the present invention, it is made possible to provide aretarder and a circular polarizer capable of functioning in a broadband, that is, in the visible light wave length region, of contributingto thinning and of contributing to reduction of planar defects occurringas a side effect with widening bandwidth. It is also possible to providea circular polarizer readily producible by roll-to-roll laminating ofthe retarder with a polarizer film. And it is also possible to provide acircular polarizer contributing to improvement in image quality of thedisplayed images when applied to any image display devices.

Having described our invention as related to the present embodiments, itis our intention that the invention not be limited by any of the detailsof the description, unless otherwise specified, but rather be construedbroadly within its spirit and scope as set out in the accompanyingclaims.

1. A retarder comprising: a substrate, and on or above the substrate afirst optically anisotropic layer formed of a composition comprising arod-like liquid-crystal compound, in which the rod-like molecules arealigned homogeneously, and substantially generating a phase differenceof π at 550 nm, and a second optically anisotropic layer formed of acomposition comprising a rod-like liquid-crystal compound, in which therod-like molecules are aligned homogeneously, and substantiallygenerating a phase difference of π/2 at 550 nm; wherein at least one ofthe rod-like liquid-crystal compounds is denoted by Formula (I) below;Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²  Formula (I) where, Q¹ and Q² respectivelydenote a polymerizable group; L¹, L², L³ and L⁴ respectively denote asingle bond or a divalent linking group provided that at least either ofL³ and L⁴ represents —O—CO—O—; A¹ and A² respectively denote C2-20spacer group, and M denotes a mesogen group; and an in-plane slow axisof the second optically anisotropic layer and an in-plane slow axis ofthe first optically anisotropic layer cross substantially at 60 degrees.2. The retarder of claim 1, wherein M in the Formula (I) is a groupdenoted by Formula (II):—(—W¹-L⁵)_(n)-W²  Formula (II) where, W¹ and W² respectively denote adivalent alicyclic group, divalent aromatic group or divalentheterocyclic group; L⁵ denotes a single bond or a linking group; and nis 1, 2 or
 3. 3. The retarder of claim 1, wherein the substrate has alongitudinal direction, the in-plane slow axis of the first opticallyanisotropic layer and the longitudinal direction of the transparentsubstrate cross substantially at +30 degrees; and the in-plane slow axisof the second optically anisotropic layer and the longitudinal directionof the transparent substrate cross substantially at −30 degrees.
 4. Theretarder of claim 3, wherein a rubbing axis for predetermining anorientation angle of the rod-like molecules in the first opticallyanisotropic layer and the longitudinal direction of the transparentsubstrate cross substantially at 30 degrees; and a rubbing axis forpredetermining an orientation angle of the rod-like molecules in thesecond optically anisotropic layer and the longitudinal direction of thetransparent substrate cross substantially at −30 degrees.
 5. Theretarder of claim 4, wherein a surface of the first opticallyanisotropic layer has the rubbing axis for predetermining an orientationangle of the rod-like molecules in the second optically anisotropiclayer.
 6. The retarder of claim 1, wherein at least one of the opticallyanisotropic layers comprises a compound denoted by Formula (V):(Hb-L²-)_(n)B¹  Formula (V) where Hb denotes a C6-40 aliphatic group oroligosiloxanoxy group having a C4-40 aliphatic group; L² represents adivalent linking group selected from the group consisting of —O—, —S—,—CO—, —NR⁵—, —SO₂—, an alkylene group, alkenylene group, arylene groupand any combinations thereof; R⁵ represents a hydrogen atom or a C1-6alkyl group; n represents an integer from 2 to 12; and B¹ represents ann-valent group containing at least three cyclic structures, so that therod-like molecules in the layer are aligned homogenously with a notgreater than 10 degrees tilt angle relative to a layer plane.
 7. Theretarder of claim 6, wherein B⁵¹ is an n-valent group denoted by Formula(V-a);(-Cy⁵¹-L⁵³-)_(n)Cy⁵²  Formula (V-a) where Cy⁵¹ is a divalent cyclicgroup; L⁵³ is a divalent linking group selected from the groupconsisting of a single bond, -alkylene-, -alkenylene-, -alkynylene-,—O—, —S—, —CO—, —NR—, —SO₂— and any combinations thereof; Cy⁵² is ann-valent cyclic group; and n is an integer from 2 to
 12. 8. A circularpolarizer comprising: a linear polarizer film having a transparent axissubstantially inclined at +45 degrees or −45 degrees relative to alongitudinal direction thereof, a substrate having a longitudinaldirection, a first optically anisotropic layer formed of a compositioncomprising a rod-like liquid-crystal compound, in which the rod-likemolecules are aligned homogeneously, and substantially generating aphase difference of n at 550 nm, and a second optically anisotropiclayer formed of a composition comprising a rod-like liquid-crystalcompound, in which the rod-like molecules are aligned homogeneously, andsubstantially generating a phase difference of π/2 at 550 nm; wherein atleast one of the rod-like liquid-crystal compounds is denoted by Formula(I) below;Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²  Formula (I) where, Q¹ and Q² respectivelydenote a polymerizable group; L¹, L², L³ and L⁴ respectively denote asingle bond or a divalent linking group provided that at least either ofL³ and L⁴ represents —O—CO—O—; A¹ and A² respectively denote a C2-20spacer group, and M denotes a mesogen group; the transparent axis of thelinear polarizer film and the longitudinal direction of the substratecross substantially at +45 degrees or −45 degrees; and an in-plane slowaxis of the second optically anisotropic layer and an in-plane slow axisof the first optically anisotropic layer cross substantially at 60degrees.
 9. The circular polarizer of claim 8, wherein M in the Formula(I) is a group denoted by denotes is denoted by Formula (II):—(—W¹-L⁵)_(n)-W²—  Formula (II) where, W¹ and W² respectively denote adivalent alicyclic group, divalent aromatic group or divalentheterocyclic group; L⁵ denotes a single bond or a linking group; and nis 1, 2 or
 3. 10. The circular polarizer of claim 8, wherein thein-plane slow axis of the first optically anisotropic layer and alongitudinal direction of the substrate cross substantially at +30degrees; and the in-plane slow axis of the second optically anisotropiclayer and the longitudinal direction of the substrate crosssubstantially at −30 degrees.
 11. The circular polarizer of claim 8,wherein a rubbing axis for predetermining an orientation angle of therod-like molecules in the first optically anisotropic layer and thelongitudinal direction of the substrate cross substantially at +30degrees; and a rubbing axis for predetermining an orientation angle ofthe rod-like molecules in the second optically anisotropic layer and thelongitudinal direction of the substrate cross substantially at −30degrees.
 12. The circular polarizer of claim 11, wherein a surface ofthe first optically anisotropic layer has the rubbing axis forpredetermining an orientation angle of the rod-like molecules in thesecond optically anisotropic layer.
 13. The retarder of claim 8, whereinat least one of the optically anisotropic layers comprises a compounddenoted by Formula (V):(Hb-L²-)_(n)B¹  Formula (V) where Hb denotes a C6-40 aliphatic group oroligosiloxanoxy group having a C4-40 aliphatic group; L² represents adivalent linking group selected from the group consisting of —O—, —S—,—CO—, —NR⁵—, —SO₂—, an alkylene group, alkenylene group, arylene groupand any combinations thereof; R⁵ represents a hydrogen atom or a C1-6alkyl group; n represents an integer from 2 to 12; and B¹ represents ann-valent group containing at least three cyclic structures, so that therod-like molecules in the layer are tilted at not greater than 10degrees relative to a layer plane.
 14. The circular polarizer of claim13, wherein B⁵¹ is an n-valent group denoted by Formula (V-a);(-Cy⁵¹-L⁵³-)_(n)Cy⁵²  Formula (V-a) where Cy⁵¹ is a divalent cyclicgroup; L⁵³ is a divalent linking group selected from the groupconsisting of a single bond, -alkylene-, -alkenylene-, -alkynylene-,—O—, —S—, —CO—, —NR—, —SO₂— and any combinations thereof; Cy⁵² is ann-valent cyclic group; and n is an integer from 2 to 12.